The first generation of microfluidic biochips contained permanently etched micropumps, microvalves, and microchannels, and their operation was based on the principle of continuous fluid flow. In contrast to continuous-flow microfluidic biochips, digital microfluidic biochips offer scalable system architecture based on a two-dimensional microfluidic array of identical basic unit cells, where the liquid is divided into independently controllable discrete droplets. The discrete droplet can be moved by various actuation methods, including thermal, surface wave, electrostatic, dielectrophoretic and, most commonly, electrowetting. For electrowetting actuation, the configuration of electrowetting-on-dielectric (EWOD) has become the choice for aqueous liquids for its reversible operations.
Digital microfluidics such as the Lab-on-a-chip (LOC) generally means the manipulation of droplets using EWOD technique. The conventional EWOD-based device generally includes two parallel glass plates. The bottom plate contains a patterned array of individually controllable electrodes, and the top plate is coated with a continuous ground electrode. Electrodes are preferably formed by a material like indium tin oxide (ITO) that has the combined features of electrical conductivity and optical transparency in thin layer. A dielectric insulator coated with a hydrophobic film is added to the plates to decrease the wettability of the surface and to add capacitance between the droplet and the control electrode. The droplet containing biochemical samples and the filler medium are sandwiched between the plates while the droplets travel inside the filler medium. In order to move a droplet, a control voltage is applied to an electrode adjacent to the droplet and, at the same time, the electrode just under the droplet is deactivated.
Over the past several years there have been advances utilizing different approaches to microfluidics based upon manipulation of individual nanoliter-sized droplets through direct electrical control. Examples of such systems can be found in U.S. Pat. No. 6,911,132 B2, entitled “Apparatus for Manipulating Droplets by Electrowetting-Based Techniques,” issued on Jun. 28, 2005 to Pamula et al.; U.S. Pat. No. 7,569,129 B2, entitled “Methods for manipulating droplets by electrowetting-based techniques,” issued on Aug. 4, 2009 to Pamula et al.; U.S. patent application Ser. No. 12/576,794, entitled “Apparatuses and methods for manipulating droplets,” filed on Oct. 9, 2009 to by Pamula et al.; U.S. Pat. No. 7,815,871 B2, entitled “Droplet microactuator system,” issued on Oct. 19, 2010 to Pamula et al.; U.S. patent application Ser. No. 11/343,284, entitled “Apparatuses and Methods for Manipulating Droplets on a Printed Circuit Board,” filed on Jan. 30, 2006 by Pamula et al.; U.S. Pat. No. 6,773,566, entitled “Electrostatic Actuators for Microfluidics and Methods for Using Same,” issued on Aug. 10, 2004 to Shenderov et al.; U.S. Pat. No. 6,565,727, entitled “Actuators for Microfluidics Without Moving Parts,” May 20, 2003, to Shenderov et al.; U.S. patent application Ser. No. 11/430,857, entitled “Device for transporting liquid and system for analyzing” filed on May 10, 2006 by Adachi et al., the disclosures of which are incorporated herein by reference. These techniques offer many advantages in the implementation of the digital microfluidics paradigm as described above but current fabrication techniques to produce these microfluidic chips still depend on rather complex and expensive manufacturing techniques. Some of these microfluidic chips are currently produced in microfabrication foundries utilizing expensive processing steps based on semiconductor processing techniques routinely used in the integrated circuit (IC) fabrication industry. In addition to higher cost for semiconductor manufacturing techniques, semiconductor foundries are not easily accessible. Some are using Printed Circuit Board technologies and claim typically to have fabrication or prototyping turn-around times of as quick as 24 hours.
Unfortunately, the conventional microfluidic systems employing microfluidic technique built to date are still highly specialized to particular applications. Many current lab-on-a-chip technologies (including both continuous-flow and digital microfluidic devices) are relatively inflexible and designed to perform only a single assay or a small set of very similar assays. The progress in microfluidic system development (including both continuous-flow and digital microfluidic devices) has been hampered by the absence of standard commercial components. Also, due to the fixed layouts of current microfluidic chips, a new chip design is required for each application, making it expensive to develop new applications. Furthermore, many of these devices are fabricated using expensive microfabrication techniques derived from semiconductor integrated circuit manufacturing. As a result, applications for microfluidic devices are expanding relatively slowly due to the cost and effort required to develop new devices for each specific application. Although batch fabrication allows microfabricated devices to be inexpensive when mass-produced, the development of new devices can be prohibitively expensive and time consuming due to high prototyping costs and long turn-around time associated with fabrication techniques. In order to broaden the range of applications and impact of microfluidics in medicine, drug discovery, environmental and food monitoring, and other areas including consumer electronics, there is a long-felt need both for microfluidic approaches which provide more reconfigurable, flexible, integrated devices, as well as techniques for more inexpensively and rapidly developing and manufacturing these chips.
Also, as more bioassays are executed concurrently on a LOC as well as more sophisticated control for resource management, system integration and design complexity are expected to increase dramatically. To establish a development path for digital microfluidics similar to the development of digital electronics requires the definition of architectural and execution concepts for assembling digital microfluidic devices into networks that perform fluidic operations in support of a diverse set of applications. Indeed, a hierarchical integrated digital microfluidic design approach is needed to facilitate scalable design for many biomedical applications. But more important than providing a totally complete set of validated microfluidic elements within a platform is the fact that all elements have to be amenable to a well established fabrication technology. The difficulty with a hierarchical approach is the lack of standard fabrication technologies and digital microfluidic device simulation libraries, which make the hierarchical design approach difficult to implement. The Microelectrode Array Architecture provides a fundamental element called “microelectrode” which is the standard component to establish a development path for digital microfluidics (similar to the CMOS transistors for the development of digital electronics) for assembling microfluidic components into networks that perform microfluidic operations. Also, microelectrodes can be implemented with well established fabrication technologies such as CMOS or thin film transistor (TFT) fabrication technologies. Moreover, because microelectrodes can be software programmed into all necessary digital microfluidic components to complete the LOC designs, batch fabrication of the “blank” chips allows microfabricated devices to be inexpensive when mass-produced.
There is a need in the art for a system and method for reducing the labor and cost associated with generating the digital microfluidic systems. The art raises the LOC designs to the applications level to relieve LOC designers from the burden of manual optimization of bioassays, time-consuming hardware design, costly testing and maintenance procedures. Through the field-programmability of the Microelectrode Array Architecture, the development of new devices could be achieved in couple hours by programming a “blank” chip based on the Microelectrode Array Architecture. So prototyping will be easy and inexpensive.
There is a need in the art for a new architecture to facilitate scalable design for generating digital microfluidic systems and new applications in the manipulation of droplets. The art is able to complete the hierarchical integrated digital microfluidic design approach which provides a path to deliver the same level of computer aided design (CAD) support to the biochip designer that the semiconductor industry now takes for granted.
There is also a need in the art for the improvement of the conventional digital microfluidic architecture that applications beyond the LOC design can be realized such as Field-programmable Permanent Display and Fluidic Micro-Crane systems.
It is believed that the Microelectrode Array Architecture can provide solutions to the needs mentioned above with a number of advantages over the conventional digital microfluidic systems.
The Microelectrode Array Architecture can be used by different digital microfluidic technologies, including EWOD but not limited to it. If this architecture is implemented based on EWOD technology, it's called the EWOD Microelectrode Array Architecture.